Laser light absorbing additive

ABSTRACT

Laser light absorbing additive comprising particles that contain at least a first polymer with a first functional group and 0-95 wt. % of an absorber, the weight percentage relating to the total of the first polymer and the absorber and the first polymer being bound in at least a part of the surface of the particles by means of the first functional group to a second functional group, which is bound to a second polymer.

This application is the US national phase of international applicationPCT/NL2003/000773 filed 6 Nov. 2003 which designated the U.S. and claimsbenefit of NL 1022081, dated 4 Dec. 2002 and NL 1023385, dated 12 May2003, the entire content of each of which is hereby incorporated byreference.

FIELD

The invention relates to a laser light absorbing additive.

BACKGROUND AND SUMMARY

Such an additive is known from WO 01/0719, in which antimony trioxidewith a particle size of at least 0.5 μm is applied as the absorber. Theadditive is applied in polymeric compositions in such a content that thecomposition contains at least 0.1 wt. % of the additive so as to be ableto apply a dark marking against a light background in the composition.Preferably a nacreous pigment is further added to obtain a bettercontrast.

The known additive has the disadvantage that in many cases, inparticular in compositions with polymers that in themselves are onlyweakly carbonizing, only a poor contrast can be obtained by laserirradiation.

The aim of the invention is, to provide an additive that, also whenmixed into polymers that in themselves are weakly carbonizing, producesa composition that is capable of being written with laser light with agood contrast.

This aim is achieved according to the invention in that the additivecomprises particles that contain at least a first polymer with a firstfunctional group and 0-95 wt. % of an absorber, the weight percentagebeing related to the total of the first polymer and the absorber and thefirst polymer being bound in at least a part of the surface of theparticles by means of the first functional group to a second functionalgroup, which is bound to a second polymer.

Upon irradiation with laser light polymeric compositions that containthe additive according to the invention area found to produce anunexpectedly high contrast between the irradiated and non-irradiatedparts. This contrast is also significantly higher than when acomposition is applied that contains only the absorber and the first orthe second polymer.

DETAILED DESCRIPTION

The additive according to the invention contains 0-95 wt. % of anabsorber. Surprisingly, it has been found that an additive that does notcontain a separate absorber and thus consists only of particles of thefirst polymer, surrounded by a layer of the second polymer bound to it,gives a significantly higher blackening under the influence of laserlight than the first polymer as such.

Preferably, however, the additive contains at least 1 wt % or more,preferably at least 2, 3, 4, 5 or 10 wt % of an absorber because thisresults in faster blackening in the additive upon radiation with laserlight.

The additive contains at most 95 wt. % of an absorber. At higherpercentages the black forming capacity tends to decrease, possibly as aconsequence of the relatively low amount of second and in particularfirst polymer present in the additive, the presence in the additive ofwhich components has been found to be crucial in the composition of theinvention as they seem to promote carbonisation as explained later.Preferably the additive contains between 5 wt % and 80 wt % of anabsorber. In this range the composition shows an optimal black formingcapacity.

As an absorber use can be made of those substances that are capable ofabsorbing laser light of a certain wavelength. In practice thiswavelength lies between 157 nm and 10.6 μm, the customary wavelengthrange of lasers. If lasers with larger or smaller wavelengths becomeavailable, other absorbers may also be considered for application in theadditive according to the invention. Examples of such lasers working inthe said area are CO₂ lasers (10.6 μm), Nd:YAG lasers (1064, 532, 355,266 nm) and excimer lasers of the following wavelengths: F₂ (157 nm),ArF (193 nm), KrCl (222 nm), KrF (248 nm), XeCl (308 nm) and XeF (351nm). Preferably Nd:YAG lasers and CO₂ lasers are used since these typeswork in a wavelength range which is very suitable for the induction ofthermal processes that are applied for marking purposes. Such absorbersare known per se, as is the wavelength range within which they canabsorb laser radiation. Various substances that may be considered foruse as an absorber will be specified below.

The activity of the additive, preferably in the form of particles of asize between 200 nm and 50 μm mixed into a polymer, seems to be based ontransmission of the energy absorbed from the laser light to the polymer.The polymer can decompose due to this heat release, with carbonremaining behind. This process is known as carbonization. The quantityof carbon that remains behind depends on the polymer. In the additivesaccording to the state of the art the heat release to the environment inmany cases appears to be insufficient to yield an acceptable contrast,in particular in the case of weakly carbonizing polymers, which upondecomposition leave little carbon behind.

Examples of suitable absorbers are oxides, hydroxides, sulphides,sulphates and phosphates of metals such as copper, bismuth, tin,aluminium, zinc, silver, titanium, antimony, manganese, iron, nickel andchromium and laser light absorbing (in)organic dyes. Particularlysuitable are antimony trioxide, tin dioxide, barium titanate, titaniumdioxide, aluminium oxide, copper phosphate and anthraquinone and azodyes.

The additive according to the invention consists substantially ofparticles comprising a first polymer with a first functional group and0-95, preferably 1-95 wt. % and more preferably 5-80 wt % of an absorbermixed into it. The weight percentage relates to the total of firstpolymer and absorber. This first polymer preferably has a polarcharacter so that it can adhere with a certain force to the, as a ruleinorganic, absorber, which as a rule also has a polar character. Thisensures that, during processing of the additive, the absorber does notmigrate to other components, to be discussed below, of compositions inwhich the additive is applied as laser light absorbing component.

The size of the additive particles in practice lies between 0.2 and 50μm. For effective absorption of the laser light the size of theseparticles is preferably equal to at least approximately twice thewavelength of the laser light to be applied later. As an additiveparticle in this respect is considered an amount of absorber, dependingon the size of the absorber particles consisting of a single or of moreabsorber particles, together with an amount of first polymer attached toit and separated from other additive particles by the second polymer.The size of a particle is understood to be the largest dimension in anydirection, so for example the diameter for spherical particles and thelength of the largest for ellipsoidal particles. A particle size of morethan twice the wavelength of the laser light admittedly leads to a lowereffectiveness in the absorption of the laser light but also to lessinfluence on the decrease of the transparency due to the presence of theadditive particles. The size preferably lies between 500 nm and 2.5 μm.

The absorber is present in the additive in the form of particles thatare smaller than the size of the additive particles. The lower limit ofthe absorber particle size is determined by the requirement that theabsorber must be capable of being mixed into the first polymer. It isknown to the person skilled in the art that this miscibility isdetermined by the total surface of a certain weight quantity of absorberparticles and the person skilled in the art will readily be able todetermine the lower limit of the particle size of the absorber to bemixed in when knowing the desired size of the additive particles and thedesired quantity of absorber to be mixed in. Generally the D₅₀ of theabsorber particles will be not smaller than 100 nm and preferably notsmaller than 500 nm. In the additive according to the invention thefirst polymer is bound in at least a part of the surface of theparticles by means of the first functional group to a second functionalgroup, which is bound to a second polymer.

Both the first and the second polymer are preferably thermoplasticpolymers, as this will facilitate mixing of the absorber into the firstpolymer and, respectively, of the additive into a matrix polymer to makeit suitable for laser writing.

The first polymer contains a first functional group and is bound bymeans of this group to a second functional group, which is bound to asecond polymer. Thus, around the surface of an additive particle a layerof a second polymer, bound to the first polymer by the respectivefunctional groups, is present, which at least partially screens off thefirst polymer in the particle from the environment around the additiveparticle. The thickness of the layer of the second polymer is notcritical and as a rule it is negligible relative to the particle sizeand amounts to for example between 1 and 10% thereof. For a secondpolymer grafted with for example 1 wt. % MA, the quantity of secondpolymer relative to the first polymer lies for example between 2 and 50wt. % and is preferably smaller than 30 wt. %. For other functionalgroups and/or other percentages of second functional groups, thequantity of the second polymer should be chosen such that a quantity ofsecond functional groups is present that corresponds to the examplegiven. As the number of second functional groups increases, the size ofthe additive particles is found to decrease.

Besides the second polymer bound to the first polymer preferably also aquantity of a third polymer that is not provided with a functionalizedgroup is present, for example a polyolefin. It is also possible tochoose the matrix polymer, into which the masterbatch is to be mixedlater, as the third polymer. If desired this matrix polymer can also beadded as a fourth polymer so as to later achieve improved mixing into alarger quantity of the matrix polymer. This is for example the case whensilicone rubbers are applied as the matrix polymer. Thisnon-functionalized third polymer may be the same as the bound secondpolymer but must at least be compatible, in particular miscible, withit. Thus, the said screening off of the first polymer in the particlefrom the environment is improved and also the mixing in of the additiveaccording to the invention, which in this case can be considered to be amasterbatch of the additive in the non-functionalized third polymer,into a matrix polymer to make it laser writable can be improved. In sucha masterbatch the proportion of the functionalized second plus thenon-functionalized third polymer preferably lies between 20 and 60 wt. %of the total of the first, the second and the third polymer and theabsorber. More preferably this proportion lies between 25 and 50 wt. %.Within said limits a masterbatch is obtained that can suitably be mixedin through melt processing. A higher proportion than the said 60% isallowable but in that case the quantity of the additive particles properin the masterbatch is relatively small.

As first and second functional groups any two functional groups can beconsidered that are capable of reacting with each other. Examples ofsuitable functional groups are carboxylic acid groups and ester groupsand the anhydride and salt forms thereof, an epoxy ring, an amine group,an alkoxy silane group or an alcohol group. It is known to the personskilled in the art in which combinations such functional groups canreact with each other. The functional groups may be present in the firstand second polymer per se, such as the terminal carboxylic acid group ina polyamide, but may also have been applied to them by for examplegrafting, as usually applied to provide for example polyolefins with afunctional group, for example leading to the polyethylene grafted withmaleic acid known per se.

Suitable first polymers are semi-crystalline or amorphous polymers thatcontain a first functional group that can react in the melt with thesecond functional group of the second polymer.

The melting point and the glass transition point, respectively, of thesemi-crystalline and the amorphous polymers, respectively, preferablylies above 120 and above 100° C., respectively, and more preferablyabove 150° C. and above 120° C, respectively. Suitable second functionalgroups are for example hydroxy, phenolic, (carboxylic) acid (anhydride),amine, epoxy and isocyanate groups. Examples of suitable second polymersare polybutylene terephthalate (PBT), polyethylene terephthalate (PET),amine-functionalized polymers including semi-crystalline polyamides, forexample polyamide-6, polyamide-66, polyamide-46 and amorphouspolyamides, for example polyamide-6I or polyamide-6T, polysulphone,polycarbonate, epoxy-functionalized polymethyl (meth)acrylate, styreneacrylonitrile functionalized with epoxy or other functional groups asmentioned above. Suitable first polymers are those with the usualintrinsic viscosities and molecular weights. For polyesters theintrinsic viscosity lies for example between 1.8 and 2.5 dl/g, measuredin m-cresol at 25° C. For polyamides the molecular weight lies forexample between 5,000 and 50,000.

To choose a suitable first polymer the person skilled in the art willprincipally be guided by the desired degree of adhesion of the firstpolymer to the absorber and the required degree of carbonizationthereof. This adhesion of the first polymer to the absorber mostpreferably is better than that of the second and third polymer (to bedefined later) to the absorber. This secures the integrity of theabsorbing additive during its processing. It is further unwanted thatthe absorber and the first polymer can chemically react with oneanother. Such chemical reactions cause degradation of absorber and/orthe first polymer leading to undesired by-products, discolouration andpoor mechanical and marking properties.

The first polymer preferably has a degree of carbonization of at least5%, defined as the relative quantity of carbon that remains behind afterpyrolysis of the polymer in a nitrogen atmosphere. At a lower degree ofcarbonization the contrast obtained upon laser irradiation decreases, ata higher degree the contrast increases until saturation occurs. It issurprising that the presence during laser irradiation of a polymer withsuch a low degree of carbonization, which in itself produces a scarcelyvisible contrast, as a compatible polymer in the additive according tothe invention already makes it possible to obtain a high contrast.Polyamides and polyesters are very suitable due to their availability ina wide range of melting points and have a degree of carbonization ofapproximately 6% and 12%, respectively. Polycarbonate is very suitablepartly due to its higher degree of carbonization of 25%. Furthermorepolyamides and polycarbonate appear to exhibit good adhesive force withmost inorganic absorbers, in particular also to aluminium oxide andtitanium dioxide. Polyamide also exhibits good adhesion to antimonytrioxide. In addition, the reaction of their, first, reactive group withfor example the MA-grafted polymers that can advantageously be appliedas grafted polymer, which will be discussed later, is irreversible underthe circumstances under which the additive is usually applied.

Suitable as the second polymer are thermoplastic polymers having afunctional group that can react with the first functional group of thefirst polymer to be applied. Particularly suitable as the second polymerare polyolefin polymers grafted with an ethylenically unsaturatedfunctionalized compound. The ethylenically unsaturated functionalizedcompound grafted on the polyolefin polymer can react with the firstfunctional group of the first polymer, for example with a terminal groupof polyamide. Polyolefin polymers that may be considered for use in thecomposition according to the invention are those homo- and copolymers ofone or more olefin monomers that can be grafted with an ethylenicallyunsaturated functionalized compound or in which the functionalizedcompound can be incorporated into the polymer chain during thepolymerization process. Examples of suitable polyolefin polymers areethylene polymers, propylene polymers. Examples of suitable ethylenepolymers are all thermoplastic homopolymers of ethylene and copolymersof ethylene with as comonomer one or more α-olefins with 3-10 C-atoms,in particular propylene, isobutene, 1-butene, 1-hexene,4-methyl-1-pentene and 1-octene, that can be prepared using the knowncatalysts such as for example Ziegler-Natta, Phillips and metallocenecatalysts. The quantity of comonomer as a rule lies between 0 and 50 wt.%, and preferably between 5 and 35 wt. %. Such polyethylenes are knownamongst other things by the names high-density polyethylene (HDPE),low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE)and linear very low-density polyethylene (VL(L)DPE). Suitablepolyethylenes have a density between 860 and 970 kg/m³. Examples ofsuitable propylene polymers are homopolymers of propylene and copolymersof propylene with ethylene, in which the proportion of ethylene amountsto at most 30 wt. % and preferably at most 25 wt. %. Their Melt FlowIndex (230° C., 2.16 kg) lies between 0.5 and 25 g/10 min, morepreferably between 1.0 and 10 g/10 min. Suitable ethylenicallyunsaturated functionalized compounds are those which can be grafted onat least one of the aforesaid suitable polyolefin polymers. Thesecompounds contain a carbon-carbon double bond and can form a side branchon a polyolefin polymer by grafting thereon. These compounds can beprovided in the known way with one of the functional groups mentioned assuitable in the above.

Examples of suitable ethylenically unsaturated functionalized compoundsare the unsaturated carboxylic acids and esters and anhydrides andmetallic or non-metallic salts thereof. Preferably the ethylenicunsaturation in the compound is conjugated with a carbonyl group.Examples are acrylic, methacrylic, maleic, fumaric, itaconic, crotonic,methyl crotonic and cinnamic acid and esters, anhydrides and possiblesalts thereof. Of the compounds with at least one carbonyl group, maleicanhydride is preferred.

Examples of suitable ethylenically unsaturated functionalized compoundswith at least one epoxy ring are, for example, glycidyl esters ofunsaturated carboxylic acids, glycidyl ethers of unsaturated alcoholsand of alkyl phenols and vinyl and allyl esters of epoxy carboxylicacids. Glycidyl methacrylate is particularly suitable.

Examples of suitable ethylenically unsaturated functionalized compoundswith at least one amine functionality are amine compounds with at leastone ethylenically unsaturated group, for example allyl amine, propenyl,butenyl, pentenyl and hexenyl amine, amine ethers, for exampleisopropenylphenyl ethylamine ether. The amine group and the unsaturationshould be in such a position relative to each other that they do notinfluence the grafting reaction to any undesirable degree. The aminesmay be unsubstituted but may also be substituted with for example alkyland aryl groups, halogen groups, ether groups and thioether groups.

Examples of suitable ethylenically unsaturated functionalized compoundswith at least one alcohol functionality are all compounds with ahydroxyl group that may or may not be etherified or esterified and anethylenically unsaturated compound, for example allyl and vinyl ethersof alcohols such as ethyl alcohol and higher branched and unbranchedalkyl alcohols as well as allyl and vinyl esters of alcohol substitutedacids, preferably carboxylic acids and C₃-C₈ alkenyl alcohols. Furtherthe alcohols may be substituted with for example alkyl and aryl groups,halogen groups, ether groups and thioether groups, which do notinfluence the grafting reaction to any undesirable degree.

Examples of oxazoline compounds that are suitable as ethylenicallyunsaturated functionalized compounds in the framework of the inventionare for example those with the following general formula

where each R, independently of the other hydrogen, is a halogen, aC₁-C₁₀ alkyl radical or a C₆-C₁₄ aryl radical.

The quantity of the ethylenically unsaturated functionalized compound inthe polyolefin polymer functionalized by grafting preferably liesbetween 0.05 and 1 mgeq per gramme of polyolefin polymer.

As the third polymer the same polymers may be considered as thosementioned above for the second polymer, albeit in theirnon-functionalized form.

The second and in particular the third polymer may contain pigments,colorants and dyes. This has the advantage that no separate colouredmasterbatch has to be added when the laser writable additive is mixedwith a matrix polymer in those cases where a coloured composition ispreferred.

The invention also relates to a process for the preparation of theadditive according to the invention, comprising the mixing of acomposition containing an absorber and a first polymer having a firstfunctional group with a second polymer containing a second functionalgroup that is reactive with the first functional group.

It has been found that in this way the additive is divided intoparticles, consisting of a mixture of the first polymer and theabsorber, which at their surface are provided with a layer of the secondpolymer, so that after mixing of the additive into a matrix polymer anoptimal contrast is obtained therein when it is laser written.

The composition containing the absorber and the first polymer can beprepared by mixing the absorber and a melt of the first polymer. Theratio between the quantity of the first polymer and the quantity ofabsorber in the composition lies between 90 vol. %: 10 vol. % and 60vol. %: 40 vol. %. More preferably this ratio lies between 80 vol. %: 20vol. % and 50 vol. %: 50 vol. %.

Said composition is mixed with a second polymer that contains a secondfunctional group that is reactive with the first functional group. Thismixing takes place above the melting point of both the first and thesecond polymer and preferably in the presence of a quantity of anon-functionalized third polymer. Third polymers that may be consideredare in particular those which have been mentioned above as the secondpolymer, but in their non-functionalized form. This third polymer doesnot need to be the same as the functionalized second polymer. Thepresence of the non-functionalized third polymer ensures adequate meltprocessability of the total mixture so that the desired homogeneousdistribution of the additive particles in the resulting masterbatch isobtained.

In the melt the functional groups react with each other and thescreening layer of the second polymer is formed at at least a part ofthe surface of the additive particles. At some point the screeningeffect of the second polymer will become predominant and any unreactedfirst polymer present in the additive particles will no longer be ableto pass to the surrounding melt. This screening effect is more effectiveas the difference in polarity between the first and second polymer islarger. In the above it was already indicated that the first polymerpreferably has a polar character. It is also preferred for the secondand third polymer to have a less polar character than the first one andmore preferably the second and third polymer are completely or almostcompletely apolar.

The size of the additive particles in the masterbatch obtained dependson the quantity of second functional groups. The lower and upper limitswithin which additive particles of a suitable size are obtained appearto be dependent on the first polymer. The particle size decreases as thequantity of second functional groups increases and vice versa. If thequantity of second functional groups is too large, this results inparticles that are too small and moreover in such a degree of binding ofthe second polymer to the first that this leads to demixing of the firstpolymer and the absorber particles. This leads to a reduction of thecontrast upon radiation of an object into which the additive has beenmixed in masterbatch form. If the quantity of second functional groupsis too small, this results in such large additive particles that aninhomogeneous pattern with undesirable coarse speckles is formed uponirradiation of an object into which the additive particles have beenmixed in masterbatch form. Furthermore the melt viscosity of the thirdpolymer influences the size of the additive particles in the formedmasterbatch. A higher melt viscosity leads to a lower particle size.With the above insights the person skilled in the art will be able,through simple experimentation, to determine the suitable quantity ofsecond functional groups within the limits already indicated therefor inthe above.

To obtain a laser writable polymer composition the additive according tothe invention is mixed into a matrix polymer. It has been found that acomposition of a matrix polymer and the additive according to theinvention can be written with better contrast with laser light than theknown compositions, in particular when the matrix polymer in itself ispoorly laser writable. The laser writability is also better than whenthe absorber as such is mixed into the matrix polymer or is mixed onlywith either the first or the second polymer by itself.

The invention therefore also relates to a laser writable composition,comprising a matrix polymer and an additive according to the inventiondistributed therein.

The advantages of the laser writable composition according to theinvention appear to full advantage in all matrix polymers but inparticular when the matrix polymer has been chosen from the groupconsisting of polyethylene, polypropylene, polyamide, polymethyl(meth)acrylate, polyurethane, polyesters thermoplastic vulcanizates, ofwhich SARLINK® is an example, thermoplastic elastomers, of whichArnitel® is an example, and silicone rubbers.

The laser writable composition according to the invention can alsocontain other additives known for enhancing certain properties of thematrix polymer or adding properties to it.

Examples of suitable additives are reinforcing materials [such as glassfibers and carbon fibers, nano-fillers like clays, includingwollastonite, and micas], pigments,dyes and colorants, fillers [such ascalcium carbonate and talcum], processing aids, stabilizers,antioxidants, plasticizers, impact modifiers, flame retardants, mouldrelease agents, foaming agents.

The amount of additive can vary from very small amounts such as 1 or 2volume % up to 70 or 80 volume % or more, relative to the volume of thecompound formed. Additives will normally be applied in such amounts thatany negative influence on the contrast of the laser marking obtainableby irradiating the composition will be limited to an acceptable extent.A filled composition that shows a remarkable good laser writability is acomposition comprising a polyamide, in particular polyamide-6, polyamide46 or polyamide 66, and talcum as a filler additive.

The laser writable composition according to the invention can beprepared by mixing the additive into the melted matrix polymer. Tofacilitate this mixing, the non-functionalized polymer, which serves asthe support in the masterbatch, preferably has a melting point that islower than or equal to that of the matrix polymer. Preferably the firstpolymer has a melting point that is at least equal to or higher thanthat of the matrix polymer. The non-functionalized polymer may be thesame as the matrix polymer or differ from it. The latter also applies tothe first polymer. Thus, it has been found that an absorber providedwith a layer of a polymer composition in which the first polymer ispolyamide and the second polymer a maleic anhydride grafted polyethyleneproduces a composition that is laser writable with high contrast bothwhen mixed into a polyamide matrix and when mixed into a polyethylenematrix. This favourable effect is achieved both in polyamide and inpolyethylene also if the first polymer is, for example, polycarbonate.

The quantity of additive depends on the desired density of the absorberin the matrix polymer. Usually the quantity of additive lies between 0.1and 10 wt. % of the total of additive and matrix polymer and preferablyit lies between 0.5 and 5 wt. % and more preferably between 1 and 3 wt.%. This gives a contrast that is adequate for most applications withoutessentially influencing the properties of the matrix polymer. If a dyeis used as the additive, it should be taken into account that startingfrom a certain concentration colouring of the matrix polymer may takeplace.

When the additive is being mixed into the matrix polymer the shape ofthe additive particles may change due to the shear forces that occur, inparticular they can become more elongated in shape, so that the sizeincreases. This increase will generally be not larger than a factor 2and if necessary this can be taken into account when choosing theparticle size for the mixing into the matrix polymer.

The additive-containing matrix polymer can be processed and shaped usingthe techniques known for thermoplastics processing, including foaming.The presence of the laser writable additive usually will not noticeablyinfluence the processing properties of the matrix polymer. In this wayalmost any object that can be manufactured from such a plastic can beobtained in a laser writable form. Such objects can for example beprovided with functional data, barcodes, logos and identification codesand they can find application in the medical world (syringes, pots,covers), in the automotive business (cabling, components), in thetelecom and E&E fields (GSM fronts, keyboards), in security andidentification applications (credit cards, identification plates,labels), in advertising applications (logos, decorations on corks, golfballs, promotional articles) and in fact any other application where itis useful or otherwise desirable or effective to apply a pattern of somekind to an object substantially consisting of a matrix polymer.

The additive according to the invention can be obtained as describedabove by mixing of the absorber with the first polymer followed bymixing of the resulting mixture with the second polymer and optionally aquantity of a non-functionalized third polymer. From the resultingthree-component mixture and, if a third polymer has also been co-mixed,from the resulting masterbatch, the additive according to the inventioncan be obtained in a pure form by removing a possibly non-bound part ofthe second polymer and the third polymer from the mixture. Suitablemethods for this are for example extraction with a solvent for thesecond and, if present, the third polymer and microfiltration. Forseparation of particles in this pure form, further denoted as minimalparticles, use is preferably made of a mixture or masterbatch in whichthe particle size of the additive lies between 500 nm and 20 μm, morepreferably between 500 nm and 10 μm and most preferably between 500 nmand 2 μm to achieve optimum absorption of laser light and to enableapplicability in very thin layers. A minimal particle consist of anadditive particle and an outer layer of second polymer that is bound tothe first polymer of the additive particle.

It has been found to be possible to apply the additive in this purifiedminimal particle shape on the surface of objects. The powder can be usedas such in the form of a coating or varnish in which the minimalparticles are stabilized in a binder. Suitable techniques known per sefor this are for example screen-printing and offset printing. Theresulting surface can then be written with a laser. The advantage ofthis method is that the additive does not need to be present in theentire object and can if desired also be applied only on those placeswhere laser writability is desired. Applications can be found in paintedplastic moulded articles with a light colour and for example in cardsfor identification and security applications.

The applied coating can, if desired, be covered with a, preferablytransparent, layer for further protection of the coating and the patternlater written into it.

The invention therefore also relates to the use of the additiveaccording to the invention, preferably in the form of minimal particles,for the application of a layer thereof on the surface of an object andto objects in which at least locally a layer is present that containsthe additive according to the invention.

Another suitable form in which the additive according to the inventioncan be applied, in particular in the form in which a second and ifdesired also a third polymer is present, is a paste or a latex, in whichparticles consisting of the additive (e.g. minimal particles or minimalparticles around which a small amount, up to 100 wt % of the totalparticle, of not-bound second polymer is present) are finely distributedin a dispersion medium that is not a solvent for the second and anythird polymer. Such a paste or latex can be obtained by mixing particlesconsisting of the additive according to the invention and preferably amasterbatch of these particles in a third polymer with a quantity of thedispersion medium, for example under high shear in a twin-screw extruderin the presence of a stabilizer known per se for this purpose thatensures that the particles do not sediment out of the paste or latex.The ratio between the quantity of dispersion medium and the quantity ofparticles or the quantity of masterbatch determines the viscosity of theresulting mixture. With a relatively small quantity of dispersion mediumand stabilizer a paste is obtained, with a relatively large quantity ofdispersion medium and stabilizer a latex. Water has been found to be avery suitable dispersion medium.

For making a paste the particle size of the additive is preferablychosen to lie between 1 and 200 μm. Preferably the particle size liesbetween 1 and 90 μm, with as advantage that effective absorption oflaser light and transparency when used in coatings can be obtained. Formaking a latex this particle size preferably lies between 50 nm and 2 μmand more preferably between 100 nm and 500 nm, so that it is suitablefor application in thin layers. Paste and latex are suitable for theapplication of, in particular water-borne, coatings on all surfaces towhich these adhere with a force that is adequate for the intendedapplication. Paste and latex according to the invention are found toadhere particularly well to paper and plastics. In this way surfaces canbe obtained which can be printed using laser light, for example inprinters provided with a laser with a suitable wavelength and withoutapplication of toners, with non-fading graphics with a high contrast,for example text or photographs. This non-fading offers a greatadvantage over the current combinations of paper and printing means. Afurther advantage of in particular paper that has been provided with alayer of the paste or latex according to the invention described aswater-borne is the possibility to recycle this paper in a water-basedsystem. A latex is preferably applied as paper coating. As coating layerfor plastic objects, for example dashboard foils, a paste is preferablyapplied.

A further suitable form in which the additive according to the inventioncan be applied is obtained by grinding a masterbatch of the additiveaccording to the invention in the third polymer, for examplecryogenically, to particles with a size between 100 μm and 1 mm,preferably to a size between 150 and 500 μm. In this form the additiveaccording to the invention can be mixed into non-melt-processablepolymers, such as crosslinked polymers or matrix polymers which degradearound their melting point or which have a very highly crystallinity.Examples of such matrix polymers are ultrahigh-molecular polyethylene(HMWPE), polypropylene oxide (PPO), fluoropolymers, for examplepolytetrafluorethylene (Teflon) and thermosetting plastics.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 show a TEM picture of laser writable composition LP7.

The invention will be elucidated on the basis of the following examples.

In the Examples and Comparative Experiments the following materials areused:

As first polymer:

-   P1-1. Polyamide K122 (DSM)-   P1-2. Polycarbonate Xantar® R19 (DSM)-   P1-3. Polybutylene terephthalate 1060 (DSM)

As the second polymer:

-   P2-1. Exact® polyethylene (DEXPlastomers) grafted with 1.1 wt. % MA-   P2-2. Fusabond® M0525D polyethylene (Dupont) grafted with 0. 9 wt. %    MA

As the third polymer:

-   P3-1. Exact 0230® polyethylene (DEXPlastomers)-   P3-2. Propylene ethylene random copolymer RA112MN40 (DSM)

As the absorber:

-   A-1. Antimony trioxide with a D₆₀ of 1 μm (Campine)-   A-2. Titanium dioxide-   A-3. Macrolex® blue/violet

As the matrix polymer:

-   M-1. Polyamide K122 (DSM)-   M-2. Polypropylene homopolymer 112MN40 (DSM)-   M-3. Arnitel® EM 400 (DSM)-   M4. Exact® 8201 polyethylene (DSM)-   M-5 Sarlink® 6135N (DSM)-   M-6 Polybutylene terephthalate 1060 (DSM)-   M-7. KE 9611 U silicone rubber (ShinEtsu)-   M-8. UVTRONIC® acrylate resin (SIPCA)

EXAMPLES I-VIII

Using a twin-screw extruder (ZSK 30 of Werner & Pfleiderer) a number ofmasterbatches, MB1-MB15, of the additive according to the invention in athird polymer were made. The absorber, first and second polymer used inthe additive and the third polymer used and the respective proportionsthereof in wt. % are shown in Table 1, as are the absorber content andthe size of the formed additive particles in the masterbatch.

Using a Haake 350 cc kneader with Banbury kneading arms MB 16 and MB 17were made by mixing MB2 with matrix polymer M7 as a fourth polymer inthe quantities given in Table 1, which also shows the size of the formedadditive particles in the final master batches M16 and M17.

The master batches MB1-MB 15 were made with a throughput of 35 kg/h atan extruder speed of 350-400 rpm. The feed zone, barrel and dietemperature of the extruder and the outlet temperature of the materialare 170, 240, 260 and 287° C., respectively, if polyamide (P1-1) is usedas the first polymer and 180, 240, 260 and 260° C., respectively, ifpolycarbonate (P1-2) or PBT (P1-3) is used as the first polymer. Masterbatches MB16 and MB17 were made at a temperature of 150° C. and akneader speed of 30-50 rpm.

TABLE 1 First Second Third Fourth Particle Polymer polymer polymerpolymer Absorber size P1-1 P1-2 P1-3 P2-1 P2-2 P3-1 P3-2 M7 A-1 A-2 A-3MB2 μm MB1 8 10 40 42   0.1–1.2 MB2 14 1.4 28.6 56 0.2–2 MB3 36 3.6 36.424 0.2–2 MB4 42 4.2 25.8 28 0.2–2 MB5 48 4.8 35.2 12 0.2–2 MB6 56 5.624.4 14 0.2–2 MB7 12 10 30 48 0.5–1 MB8 14 1.4 28.6 56 0.2–2 MB9 12 1030 48 MB10 12 7.5 32.5 48 MB11 12 5 35 48 MB12 12 2.5 37.5 48 MB13 32.463.2 42.7 21.64 MB14 39.08 3.9 47.26 9.76 MB15 25.8 4.2 42 28 MB16 60 40MB17 50 50

EXAMPLE II AND COMPARATIVE EXPERIMENT A

Using a number of master batches from the previous Example a number oflaser writable compositions, LP1-LP41, were prepared by mixing differentquantities of masterbatch/pigment material into different matrixpolymers on the aforesaid extruder and kneader, respectively.Compositions containing PA, PP, Arnitel, Exact, Sarlink and PBT weremade with a ZSK 30 having feed zone, barrel, die and outlet temperatureof the extruder as given below. The compositions containing Siliconerubber were made with a Haake kneader having kneader and outlettemperature as given below. In the compositions containing Acrylateresin the additive was applied in the form of minimal particles and thecompositions were in a Dispermat mixer having mixing and outlettemperature as given below:

M-1 (PA): 160, 200, 220, 265 M-2: (PP): 160, 200, 210, 225 M-3:(Arnitel): 160, 200, 220, 237 M-4: (Exact): 100, 120, 150, 158 M-5:(Sarlink): 160, 180, 220, 225 M-6: (PBT): 180, 230, 240, 265 M-7.(Silicone rubber): 150, 150 M-8. (Acrylate resin): 20, 60

Table 2 gives the proportions of the different components in wt. %.

The compositions obtained were injection moulded to form plates with athickness of 2 mm. On the plates a pattern was written using a diodepumped Nd:YAG UV laser of Lasertec, wavelength 355 nm, and a diodepumped Nd:YAG IR laser of Trumpf, type Vectomark Compact, wavelength1064 nm.

For comparison purposes similar plates were also made and written thathad been manufactured from compositions containing only the thirdpolymers (CP-A-CP-G) and a number that had been manufactured by mixing amasterbatch of the absorber in only polyamide into a matrix polymer(CP-H-CP-M) under the conditions as given above, the temperature profileused being that of the masterbatch or that of the matrix polymer, ifthat has a higher melting point than the polymer in the masterbatch.

The degree to which the different materials are laser writable,expressed in qualitative contrast values, is shown in Table 2. Thecontrast measurements were carried out with a Minolta 3700DSpectrophotometer with the following settings: CIELAB, light source 6500Kelvin (D65), spec colour included (SCI) and angle of measurement 10°.The laser settings were continually optimized to the maximum feasiblecontrast at the used wavelengths of 355 and 1064 nm.

From the results it is clear that the plates manufactured from materialscontaining the additive according to the invention can be written with alaser with a considerably better result than compositions in which noabsorber is present or in which a masterbatch of an absorber mixed intoonly a first and a third polymer (in this case equal to the first) isapplied.

FIG. 1 shows a TEM picture of laser writable composition LP7.

TABLE 2 A-1: M-7: Master- Master- Antimony M-1: M-2: M-3: M-4: M-5: M-6:Silicone Contrast Contrast Composition batch batch trioxide PA PPArnitel Exact Sarlink PBT Rubber 355 nm 1064 nm MB1 MB2 LP1 10 4.2 90••••• ••••• LP2 10 4.2 90 ••••• ••••• LP3 10 4.2 90 ••••• ••••• LP4 104.2 90 ••••• ••••• LP5 10 4.2 90 ••••• ••••• LP6 5 2.8 95 ••••• •••••LP7 5 2.8 95 ••••• ••••• LP8 5 2.8 95 ••••• ••••• LP9 5 2.8 95 •••••••••• LP10 5 2.8 95 ••••• ••••• LP11 3 1.68 97 ••••• ••••• LP12 3 1.6897 ••••• ••••• LP13 3 1.68 97 ••••• ••••• LP14 3 1.68 97 ••••• •••••LP15 3 1.68 97 ••••• ••••• LP16 1 0.56 99 ••• ••• LP17 1 0.56 99 ••• •••LP18 1 0.56 99 •••• ••• LP19 1 0.56 99 ••• ••• LP20 1 0.56 99 ••• •••LP21 3 1.68 97 ••••• ••••• LP22 2 1.12 98 ••••• ••••• LP23 1 0.56 99••••• ••••• LP24 0.5 0.28 99.5 •••• •••• MB8 MB12 LP25 10 4.2 90 •••••••••• LP26 5 2.8 95 ••••• ••••• LP27 3 1.68 97 ••••• ••••• LP28 2 1.1298 ••••• ••••• LP29 1 0.56 99 •••• •••• LP30 2 0.96 98 ••••• ••••• MB13MB14 LP31 5 1.082 95 ••••• ••••• LP32 3 0.649 97 •••• •••• LP33 11 1.07489 •••• •••• LP34 7.5 0.733 92.5 ••• ••• MB15 MB17 LP35 5 1.4 95 ••••• —LP36 3 0.84 97 ••••• — LP37 2 0.56 98 •••• — LP38 1 0.28 99 •••• — LP3910 2.8 90 ••••• ••••• LP40 5 1.4 95 ••••• ••••• LP41 3 0.84 97 •••••••••• CP A 100 • • CP B 100 — — C 100 • • D 100 — — E 100 • • F 100 • •G 100 — — CP H 0.8 99.2 • •• I 0.8 0.2 99 — • J 0.8 0.2 99 • • K 0.8 0.299 — • L 0.8 0.2 99 • • M 0.8 0.2 99 • ••• Qualification of contrast:Very poor contrast and granular — Poor contrast • Moderate contrast ••Good contrast ••• Very good contrast •••• Excellent contrast •••••

EXAMPLE III

Of two master batches, MB2 and MB15, additive particles consisting ofthe first polymer P1-1 and the absorbers A-1 and A-2, respectively, wereseparated from the third polymer. For this purpose the masterbatchesMB15 and MB2 were dissolved in decalin in an autoclave at 140-145° C.and separated at that temperature by means of centrifuging. Theresulting additive particles were distributed in concentrations of 20,10 and 5 wt. % in an acrylate resin (UVTRONIC® of SICPA), stabilizedwith Disperbyk® (of BYK). The resulting mixture was applied by offsetprinting on a polyester support. The compositions with the additiveparticles obtained from MB2 are referred to as LP42-LP 44, those withthe from MB15 as 45-LP 47, the successive compositions containing 20, 10and 5 wt. % additive particles, respectively.

The degree to which the different materials are laser writable wasdetermined as in Example II for the wavelengths 355 and 1064 nm and isshown in Table 3, expressed in qualitative contrast values.

TABLE 3 Matrix polymer First M-8: Absorber: Absorber: polymer:Wavelength: Composition Acrylate resin A-1 A2 P1-1 355 1064 LP42 80 16 4••••• ••••• LP43 90 8 2 •••• •••• LP44 95 4 1 •• •• LP45 80 8 12 ••••• —LP46 90 4 6 •••• — LP47 95 2 3 •• —

1. Laser light absorbing additive particles comprising: a supportparticle comprised of at least a first polymer having a first functionalgroup and an absorber in an amount between 1-95 wt. % based on totalweight of the first polymer and the absorber, wherein the absorber is atleast one selected from the group consisting of oxides, hydroxides,sulphides, sulphates and phosphates of metals, and a layer surroundingthe support particle which is comprised of a second polymer having asecond functional group, wherein the layer of the second polymer isbound to the first polymer at a surface of the support particle thereofby means of the first and second functional groups.
 2. Additiveparticles according to claim 1, further comprising a third polymer. 3.Additive particles according to claim 1, in which the second functionalgroup has been bound to the second polymer by grafting.
 4. Additiveparticles according to claim 1, in which the first functional group is aterminal group of the first polymer.
 5. Additive particles according toclaim 1, in which the second polymer is a polyolefin.
 6. Additiveparticles according to claim 1, in which the first polymer iscarbonizable to a degree of carbonization of at least 5%.
 7. Additiveparticles according to claim 6, in which a third polymer is alsopresent.
 8. Process for the preparation of the laser light absorbingadditive particles according to claim 1, comprising mixing of acomposition containing the absorber and the first polymer having thefirst functional group with the second polymer containing the secondfunctional group that is reactive with the first functional group. 9.Process according to claim 8, in which a third polymer is present duringthe mixing.
 10. Laser writable composition, comprising a matrix polymerand additive particles according to claim 1 distributed therein. 11.Laser writable composition according to claim 10 comprising 0.1 to 10wt. % of the additive particles.
 12. Laser writable compositionaccording to claim 11, comprising 0.5 to 5 wt. % of the additiveparticles.
 13. Laser writable composition according to claim 12comprising 1 to 3 wt. % of the additive particles.
 14. An object havinga surface which is provided with a laser writable layer that at leastpartly comprises the additive particles according to claim
 1. 15. Objectaccording to claim 14, wherein at least 80% of the surface consists of apolymer.
 16. Object according to claim 14, having a surface wherein atleast a part of the surface consists of paper.
 17. Paste or latexcontaining the additive particles according to claim 1 in a dispersionmedium.
 18. Paste or latex according to claim 17, in which thedispersion medium is water.